First release of images demonstrates Euclid space telescope's potential

Two things are needed to understand how the universe came into being and how it has evolved to its present form. Cosmological computer models employ the laws of physics to depict the universe's expected appearance today, while observations made with telescopes check whether these models are correct.

The Euclid Space Telescope, for the first time, will have the capability to measure the positions of billions of galaxies in three dimensions, spanning almost the entire observable universe from Earth. The first scientific images have now been published.

Euclid, the European Space Agency's (ESA) latest space telescope, has published its first color images from space. These images result from the combination of data from its two instruments: VIS (Visible Instrument) and NISP (Near-Infrared Spectrograph and Photometer), designed to capture visible and near-infrared light using large-area detectors. Euclid's most important task is to conduct the most detailed three-dimensional mapping of the universe, thereby unlocking some of its dark secrets.

The German members of the Euclid consortium, including the Max Planck Institutes for Astronomy and Extraterrestrial Physics, have developed key technical components of the telescope. They also provide logistical services for managing the immense data streams and ensure the quality of the published data.

Previous space telescopes, such as Hubble or James Webb, were built to examine very small areas of the sky in great detail. Euclid, on the other hand, broadens the view with equally high image quality: thanks to its large optics, its sensitive instruments and its position outside the disturbing Earth's atmosphere, it delivers images of large sections of the sky in a relatively short observation time, which are also remarkably sharp and contain the faint light of distant galaxies.

With the published images, members of the Euclid consortium demonstrate the full potential of Euclid using five selected objects. Each image covers an area slightly larger than the full moon. By the mission's end, approximately 40,000 such image sections will be merged, forming a vast area of about 14,000 square degrees in the sky. This constitutes one-third of the entire sky, excluding our own galaxy, the Milky Way.

The images that have now been released show one thing very clearly: each image will be a treasure trove of new insights into the physics of individual stars, the Milky Way or distant galaxies.

"The telescope will collect enormous amounts of data and detect more objects than previously possible," says Maximilian Fabricius from the Max Planck Institute for Extraterrestrial Physics in Garching near Munich and the Ludwig Maximilian University of Munich. Knud Jahnke, instrument scientist at the Max Planck Institute for Astronomy in Heidelberg, confirms, "We all need to adapt to the wealth of information that Euclid will provide."

One example is the Perseus galaxy cluster. These galaxy clusters stand as some of the largest and most massive structures in the universe. Without dark matter networks, the galaxies depicted here would be evenly distributed across the sky. "With Euclid's huge field of view and its exceptional sensitivity, the galaxies within the Perseus galaxy cluster can be measured down to their outermost and faintest regions," explains Matthias Kluge, a scientist at the Max Planck Institute for Extraterrestrial Physics and at Ludwig-Maximilians-Universität.

"There are also other galaxies in the same image that are not connected to the Perseus cluster. The further you look into the universe, the older galaxies you will find, given the finite speed at which light travels, and the more galaxies you will find at various stages of development. This wealth of information will significantly contribute to researchers' understanding of the universe's early days, marked by the abundant collisions and mergers of galaxies."

Approximately 95% of our universe appears to consist of mysterious "dark" elements, which also play a part in the formation of the Perseus galaxy cluster. While dark matter determines the gravitational effect between and within galaxies and initially slowed down the expansion of the universe, dark energy is driving the current accelerated expansion of the cosmos. However, the nature of dark matter and dark energy remains elusive.

What scientists do know is that these substances cause subtle alterations in the appearance and movements of observable objects through telescopes. To detect the "dark" influence on the visible universe, Euclid will observe the shapes, distances, and movements of billions of galaxies up to 10 billion light years away over the next six years.

Here, the spectral information from the NISP infrared instrument is supplemented with optical spectra from ground-based telescopes, which will very accurately determine the distances and movements of the galaxies imaged by Euclid and translate Euclid's two-dimensional photos into the most comprehensive three-dimensional map of the visible universe ever created.